Can large scale open ocean iron fertilisation help stop global warming?

Humans are responsible for the current rapid increases in levels of carbon dioxide (CO2) and other greenhouse gases in the atmosphere and the build up of these gases is causing global warming. We have two possible ways of slowing the rising levels of greenhouse gases in the atmosphere. We can either reduce our emissions of greenhouse gases in line with the Kyoto Protocol or we can remove carbon dioxide from the atmosphere by increasing the ability of the Earth to store carbon over the long term.

Land plants are important carbon stores and many of the suggestions on how to increase carbon storage on land have concentrated on reducing the rate at which forests are being lost and by planting new trees. Storing more carbon in the oceans has also been considered. People have suggested that adding iron to large areas of the oceans would increase phytoplankton growth and the resulting increase in photosynthesis would cause a decrease in the levels of carbon dioxide in the atmosphere. We now have the technical capacity to do large scale open ocean iron fertilisation, but do we have the knowledge and wisdom to determine whether it is acceptable to use the oceans in this way?

Reasons for large scale iron fertilisation

once the phytoplankton die, they will sink out of the surface waters taking the carbon with them and this carbon will be stored in the deep ocean for centuries.

more phytoplankton means more food for other species, more fish and more food for the growing human population.

Supporters also state that deliberate ocean iron fertilisation is simply using the oceans in the same way as we used the land for agriculture and is a very cheap option for carbon removal compared to other current alternatives. They also believe that it will not harm the environment and is a long term solution to global warming. They suggest that the carbon stored in the deep ocean could be sold as credits in the global carbon marketplace.

Reasons against large scale iron fertilisation

Scientific iron fertilisation experiments show that adding iron to the High Nitrate Low Chlorophyll (HNLC) regions of the oceans does lead to and increase in phytoplankton growth. However these experiments have also show that:

microbial activity associated with low oxygen levels may produce potent greenhouse gases such as methane (62 times more powerful a greenhouse gas than carbon dioxide) and nitrous oxide (275 times more powerful than carbon dioxide).

to have any benefit as a way to store carbon, iron fertilisation needs to be done in the Southern Ocean as this is the only HNLC region where the water sinks to the deep ocean taking carbon with it.

1. Two possible outcomes of deliberate ocean iron fertilisation. Supporters claim that adding iron would increase carbon dioxide uptake by the ocean and would encourage a healthy marine biological community. Those against iron fertilisation suggest that it would not significantly change the ability of the ocean to take up carbon dioxide and would fundamentally damage the marine ecosystem. Thank you to Ken Buesseler at Woods Hole Oceanographic Institution for allowing us use this image.

What should we do?

People have already suggested that large scale ocean iron fertilisation could be used to reduce carbon dioxide levels in the atmosphere and it is currently possible for anyone to try to do this. However scientific studies show that adding iron would only reduce carbon dioxide levels by 16% at best. It would also change the ecology of the oceans and we don't know the long term consequences of this.

We all need to think about the implications of iron fertilisation as the ocean is so important to us and to our climate. Should individuals be able to add iron to the oceans or do we need international agreements between countries? Should scientists decide what to do or should the views of industry also be considered? Are there better ways to tackle the problems of global warming?